Nanopatterned templates from oriented degradable diblock copolymer thin films

ABSTRACT

A nanopatterned template for use in manufacturing nanoscale objects. The nanopatterned template contains a nanoporous thin film with a periodically ordered porous geomorphology which is made from a process comprising the steps of: (a) using a block copolymerization process to prepare a block copolymer comprising first and second polymer blocks, the first and second polymer blocks being incompatible with each other; (b) forming a thin film under conditions such that the first polymer blocks form into a periodically ordered topology; and (c) selectively degrading the first polymer blocks to cause the thin film to become a nanoporous material with a periodically ordered porous geomorphology. In a preferred embodiment, the block copolymer is poly(styrene)-poly(L-lactide) (PS-PLLA) chiral block copolymer, the first polymer is poly(L-lactide), and the second polymer is polystyrene. Experimental results show that the first polymer blocks can be formed into a hexagonal cylindrical geomorphology with its axis perpendicular to a surface of the thin film. After hydrolysis to selectively degrade the first polymer blocks, a thin film having a series of repeated nanoscale hexagonal-cylindrical channels is obtained.

FIELD OF THE INVENTION

[0001] The present invention relates to a novel method for makingnanopatterned templates which can be subsequently used for preparingnanoscale industrial objects. More specifically, the present inventionrelates to a novel method which utilizes oriented degradable diblockcopolymer thin films to form nanopatterned templates. The nanopatternedtemplates so formed from the method of the present invention can also bereferred to as “nanoreactors”, which are articles containing a series ofperiodic nanostructured porous channels that can be used as molds,masks, or other types of templates, to subsequently manufacture productsin nanoscale dimensions. The nanopatterned templates of the presentinvention can be advantageously and cost-effectively manufactured whichcan be subsequently utilized in healthcare, semiconductor, as well asmany other industrial applications.

BACKGROUND OF THE INVENTION

[0002] In recent years, the science involving the manufacturing andapplications of nano-dimensioned (“nanomaterials”) has become one of themost promising and creative research areas. One convenient way toprepare materials in nanoscale dimension is to provide nanopatternedtemplates, i.e., “nanopatterns” with periodic porous nanostructuredarticles, for the growth of nanomaterials. These nanopatterned templatescan be considered as “nanoreactor” for producing nanomaterials. Morerecently, extensive studies to exploit the concept of nanoreactors havebeen carried out in different research areas, and wide varieties ofnanomaterials and nanoarrays have thus been obtained. Different methodsfor nanopatterning such as photolithography, soft lithography, scanningprobe lithography, electronlithography (i.e., top-down methods) andself-assembly of living cells, surfactants, dendrimers and blockcopolymers (i.e., bottom-up methods) have been proposed and examined.For a recent review, see C. Park, J. Yoon, E. L. Thomas, Polymer 2003,44, 6725-6760.

[0003] Among these studies, the formation of nanopatterns from theself-assembly of block copolymers driven by the immiscibility betweenthe constituted blocks can be efficiently, economically achieved due tothe ease of processing. Examples of this study can be found in Bates, F.S.; Fredrickson, G. H. Annu. Rev. Phys. Chem. 1990, 41, 525-557. Forsuch nanopatterns to prove useful in nanoapplications, it is necessaryto generate thin-film samples with well-oriented periodic arrays overlarge area. Different approaches to control over the orientation ofphase-separated microdomains (MD) have been achieved by using (1)solution casting, see, e.g., G. Kim, M. Libera, Macromolecules 1998, 31,2569-2577; P. Mansky, C. K. Harrison, P. M. Chaikin, R. A. Register, N.Yao, Appl. Phys. Lett. 1996, 68, 2586-2588; and R. G. H. Lammertink, M.A. Hempenius, J. E. van der Enk, V. Z.-H. Chan, E. L. Thomas, G. J.Vansco, Adv. Mater. 2000, 12, 98-103; (2) shear fields, see, e.g., G.Kim, M. Libera, Macromolecules 1998, 31, 2569-2577; P. Mansky, C. K.Harrison, P. M. Chaikin, R. A. Register, N. Yao, Appl. Phys. Lett. 1996,68, 2586-2588; and R. G. H. Lammertink, M. A. Hempenius, J. E. van derEnk, V. Z.-H. Chan, E. L. Thomas, G. J. Vansco, Adv. Mater. 2000, 12,98-103; (3) electric fields, see, e.g., T. L. Morkved, M. Lu, A. M.Urbas, E. E. Ehrichs, H. M. Jaeger, P. Mansky, T. P. Russell, Science1996, 273, 931-933; and T. Thurn-Albrecht, J. Schotter, G. A. Kästle, N.Emley, T. Shibauchi, L. Krusin-Elbaum, K. Guarini, C. T. Black, M. T.Tuominen, T. P. Russell, Science 2000, 290, 2126-2129; (4) patternedsubstrates, see, e.g., P. Mansky, Y. Liu, E. Huang, T. P. Russell, C. J.Hawker, Science 1997, 275, 1458-1460; E. Huang, L. Rockford, T. P.Russell, C. J. Hawker, Nature 1998, 395, 757-758; L. Rockford, Y. Liu,P. Mansky, T. P. Russell, Phys. Rev. Lett. 1999, 82, 2602-2605; and J.Heier, J. Genzer, E. J. Kramer, F. S. Bates, G. Krausch, J. Chem. Phys.1999, 111, 11101-11110; (5) temperature gradients, see, e.g., T.Hashimoto, J. Bodycomb, Y. Funaki, K. Kimishima, Macromolecules 1999,32,952-954; and (6) epitaxial crystallization, see, e.g., J. C.Wittmann, B. Lotz, Prog. Polym. Sci. 1990, 15, 909-948; C. De Rosa, C.Park, E. L. Thomas, B. Lotz, Nature 2000, 405,433-437; and R.-M. Ho,P.-Y. Hsieh, W.-H. Tseng, C.-C. Lin, B.-H. Huang, B. Lotz Macromolecules2003, 36, 9085-9092.

[0004] Recently, a very rapid route to generate oriented Microdomainsfor use as a water-permeable membrane by spin coating forpoly(styrene)-b-poly(ethyleneoxide) (PS-PEO) has been reported; withinseconds, arrays of nanoscopic cylindrical domains of PEO were producedin a glassy PS matrix to open a novel route towards water permeablemembranes with well-defined channel size. Their results are reported inZ. Q. Lin, D. H. Kim, X. D. Wu, L. Boosahda, D. Stone, L. LaRose, T. P.Russell, Adv. Mater. 2002, 14, 1373-1376. It has also been reported thatblock copolymers containing polyesters become the novel families for thepreparation of nanoporous materials where polyester blocks might beselectively degraded, particularly by hydrolysis treatment, see, e.g.,H. Tsuji, Y. Ikada, J. Polym. Sci., Part A: Polym. Chem., 1998,36,59-66; and A. S. Zalusky, R. Olayo-Valles, C. J. Taylor, M. A.Hillmyer, J. Am. Chem. Soc. 2001, 123, 1519-1520. In the later article,it was also reported that ordered nanoporous polymers frompoly(styrene)-b-poly(D,L-lactide) (PS-PLA) block copolymers has beensuccessfully achieved by simply chemical etching of the PLA in the bulk.

SUMMARY OF THE INVENTION

[0005] The primary object of the present invention is to develop animproved method for making industrial objects with nanoscale dimensions,or nanomaterials. More specifically, the primary object of the presentinvention is to develop an improved method for preparing nanopatternedtemplates, which can be subsequently utilized for making nanomaterials.

[0006] In the present invention, it was discovered that large-scale,well-oriented nanochannel arrays in the form of thin films can beefficiently and cost-effectively produced by using degradable blockcopolymers. In some of the preferred embodiments the details of whichwill be discussed below, a series of degradable block copolymers,poly(styrene)-b-poly (L-lactide) (PS-PLLA), with PLLA hexagonal cylinder(HC) morphology has been synthesized. By selecting appropriate solventfor spin coating, the formation of large-size, oriented microdomains ofPS-PLLA thin films where the axis of hexagonal cylinder morphology isperpendicular to the substrate (i.e., perpendicular morphology) wassuccessfully achieved. Subsequently, nanopatterned templates wereprepared after hydrolysis treatment.

[0007] Bulk samples of block copolymers were prepared by solutioncasting from dichloromethane (CH₂Cl₂) solution (10 wt % of PS-PLLA) atroom temperature. Hexagonal cylinder nanostructures of amorphous PS-PLLAwere identified by Transmission electron microscopy (TEM) andsmall-angle X-ray scattering (SAXS). Similar results for various PS-PLLAsamples having different molecular weights were also obtained. Thinfilms of the block copolymer were formed on different substrates bysimply spin coating from dilute chlorobenzene (C₆H₅Cl) solution (1.5 wt% of PS-PLLA) at room temperature without further treatment.Well-oriented, perpendicular Microdomains was obtained as evidenced byscanning probe microscopy (SPM). The effect of alignment was furtherconfirmed by the TEM images where the projected images reflectedperpendicular cylinders on the substrate. As evidenced by selected areaelectron diffraction experiments, no crystalline diffraction wasidentified; suggesting that amorphous or low crystallinity samples wereobtained after spin coating. With the process of the present invention,the oriented microdomains can be as large as several cm² in area.

[0008] The method of the present invention can be tailored for greatvarieties of end use applications. For example, different substratesincluding glass slide, carbon-coated glass slide, indium tin oxide (ITO)glass, silicon wafer, silicon oxide, inorganic light emitted diode andalumina have been used for nanopatterning. Large-size, orientedperpendicular Hexagonal cylinder morphology was obtained. However, thebottom morphology of the nanopatterns appeared well-definednanostructures under SPM examination only if the film was treated byhydrolysis (i.e., degradation of PLLA); suggesting that there is alwaysa thin layer of PLLA formed on the substrate after spin coating (forinstance, ca. 5 nm as estimated by volume fraction for cast film onglass slide having 50 nm thickness). Similar to the recent studies ofelectric field alignment of block copolymers; the surface effect fromcoated substrate on morphology is always existent. The effects ofsubstrate affinity and interfacial energy have been examined in thisstudy. The surface tension of PLLA (˜38.27 mN/m) is lower than that ofPS (˜40 mN/m) besides the affinity of PLLA with hydrophilic substrate isslightly higher than that of PS. As a result, PLLA favors topreferentially segregate on the substrate so as to form PLLA thin layer.The formation of PLLA thin layer can be avoided by spin-coating thesamples at temperature above T_(g,PLLA) but below T_(g,PS). The behaviorhas also been observed in different cases; the glass transitiontemperature of at least one of the blocks should be below processingtemperature in order to ease the substrate influence. As a result, thenanopatterned textures were thus schematically illustrated in FIG. 3A.Furthermore, the oriented nanostructures started losing orientationafter long-time annealing at temperature above PLLA crystalline melting.As a result, we speculate that the ignorance of substrate effect is dueto the kinetic effect under spinning to create a meta-stable morphology.Nevertheless, the oriented nanostructures can be fixed by simplyoxidizing the PS matrix using RuO₄. After oxidation, the PS nanopatternscan be used at service temperatures above 250° C. Our preliminaryresults indicate that the oriented effect for block copolymernanostructures is primarily attributed to the selection of appropriatesolvent evaporation rate and its solubility between constituted blocks.Similar to solution casting approach, oriented perpendicular Hexagonalcylinder morphology was formed at intermediate evaporation rate forselective solvent. The studies of detailed mechanisms for the inducedorientation are still in progress.

[0009] The method of the present invention can be utilized to extend theapplicability of nanopatterns. It is possible to have tunable filmthickness and dimension for nanopatterning. Reasonably wide range offilm thickness from 20 nm to 160 nm can be obtained by simplycontrolling the spin rate of coating as expected. Oriented PS-PLLAsamples can be achieved regardless of thin-film thickness. Also, thesurface topography of formed nanopatterns is very smooth; the averagedroughness is in the range of 0.4 nm by SPM roughness evaluation.Different domain sizes as determined by TEM, SAXS and SPM were obtainedby controlling molecular weight of PS-PLLA. Following the successfulprocedure for hydrolysis of PLA, well-oriented, perpendicular hexagonalcylinder nanochannel arrays were simply obtained within hour by using asodium hydroxide solution of methanol/water (0.5M solution was preparedby dissolving 2 g of sodium hydroxide in an 40/60 (by volume) solutionof methanol/water) at 60° C. for the degradation of amorphous PLLA.Consequently, nanopatterned templates over large area in addition touniform surface with controlled thickness and domain size in the form ofthin films were successfully prepared on different substrates.

[0010] In summary, in the present invention, we have presented anexcellent and quick way to prepare large-scale microdomains for PS-PLLAdiblock copolymers. Owing to the hydrolysis character of the polyestercomponents, the formation of the ordered nanohole arrays provides asimple path to prepare nanopatterned templates for nanoapplications.

BRIEF DESCRIPTION OF THE DRAWING

[0011] The present invention will be described in detail with referenceto the drawing showing the preferred embodiment of the presentinvention, wherein:

[0012]FIG. 1A is a TEM micrograph of solution-cast PS365-PLLA109(ƒ_(PLLA) ^(ν)=0.26) bulk sample quenched from microphase-separatedmelt; the samples were micro-sectioned by microtome and the microdomainsof PS component appear relatively dark after staining by RuO₄, while themicrodomains of PLLA component appear light

[0013]FIG. 1B show the corresponding azimuthally integratedone-dimensional SAXS profile; the result suggests a HC nanostructureswhere scattering peaks occurred at q*ratio of 1:v3:v4:v7:v9.

[0014]FIG. 2A shows the tapping-mode SPM phase image of the surface ofspin coated PS365-PLLA109 (ƒ_(PLLA) ^(ν)=0.26) thin film oncarbon-coated glass slide. As observed, the phase image exhibitsapproximately the cross-section view of hexagonally packed cylindricaltexture of which dark PS matrix indicates less phase delay than brightPLLA dispersed domains.

[0015]FIG. 2B is a direct viewing TEM image of the spin-coated thin filmafter staining with RuO₄.

[0016]FIG. 3A is a 3-D schematic illustration of PS-PLLA nanopatternprepared by spin coating.

[0017]FIGS. 3B and 3C are: (b) before hydrolysis and (c) afterhydrolysis, respectively of the tapping-mode SPM height images of thesurfaces of spin coated PS365-PLLA109 (ƒ_(PLLA) ^(ν)=0.24) thin films onglass slides.

[0018]FIGS. 4A, 4B, and 4C are the TEM micrographs of solution-cast of(a) PS83-PLLA41 (ƒ_(PLLA) ^(ν)=0.34); (b) PS198-PLLA71 (ƒ_(PLLA)^(ν)=0.27) and (c) PS280-PLLA97 (ƒ_(PLLA) ^(ν)=0.31) bulk samplesquenched from microphase-separated melt, respectively. The samples weremicrosectioned by microtome, and then stained by RuO₄ to obtainmass-thickness contrast. The corresponding azimuthally scannedone-dimensional SAXS profiles are also obtained as shown in FIGS. 4D,4E, and 4F, respectively.

[0019]FIGS. 5A, 5B, 5C, and 5D are the tapping-mode SPM phase images ofthe surfaces of spin-coated PS365-PLLA109 (ƒ_(PLLA) ^(ν)=0.24) thinfilms on (a) glass slide; (b) carbon-coated glass slide; (c) indium tinoxide (ITO) glass; (d) silicon wafer.

[0020]FIGS. 6A and 6B are the tapping-mode SPM height images of thebottom morphology for spin-coated PS365-PLLA109 (ƒ_(PLLA) ^(ν)=0.24)thin film on glass slide (a) before hydrolysis; and (b) afterhydrolysis, respectively.

[0021]FIGS. 7A, 7B, 7C, and 7D are the tapping-mode SPM phase images ofthe surfaces of spin coated PS365-PLLA109 (ƒ_(PLLA) ^(ν)=0.24) thinfilms on glass slide by using different solvents for spin coating: (a)dichlorobenzene (vapor pressure at 20° C.: 0.52 mm Hg); (b)chlorobenzene (vapor pressure at 20° C.: 12 mm Hg); (c) toluene (vaporpressure at 20° C.: 22 mm Hg); (d) THF (vapor pressure at 20° C.: 131.5mm Hg), respectively.

[0022]FIGS. 8A, 8B, and 8C are the tapping-mode SPM phase images of thesurfaces of spin coated PS365-PLLA109 (ƒ_(PLLA) ^(ν)=0.24) thin films onglass slide from chlorobenzene with different thin-film thickness: (a)160 nm; (b) 80 nm; (c) 50 nm; (d) 30 nm, respectively.

[0023]FIG. 9A is a plot of film thickness versus spin rate forspin-coated PS365-PLLA109 (ƒ_(PLLA) ^(ν)=0.26) thin films on glassslides. Open circle indicates the sample thickness measured by SPMwhereas open triangle indicates the thickness measured by depthprofiler.

[0024]FIG. 9B is the 3D tapping-mode SPM height image of SPM forspin-coated PS365-PLLA109 (ƒ_(PLLA) ^(ν)=0.26) thin film afterhydrolysis.

[0025]FIGS. 10A and 10B show FESEM micrographs of hydrolyzedPS365-PLLA109 (ƒ_(PLLA) ^(ν)=0.26) samples by viewing parallel to thecylindrical axes.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0026] The present invention will now be described more specificallywith reference to the following examples. It is to be noted that thefollowing descriptions of examples, including the preferred embodimentof this invention, are presented herein for purposes of illustration anddescription, and are not intended to be exhaustive or to limit theinvention to the precise form disclosed.

EXAMPLE 1

[0027] Synthesis of 4-Hydroxy-TEMPO-Terminated Polystyrene (PS-2)

[0028] A mixture of styrene (46 mL, 400 mmol), BPO (0.39 g, 1.6 mmol)and 4-OH-TEMPO (0.33 g, 1.92 mmol) (molar ratio of 4-OH-TEMPO/BPO =1.2)was preheated in a round-bottom flask (250 mL) in nitrogen atmosphere at95° C. for 3 h to allow BPO to decompose completely. The system was thenheated at 130° C. for another 4 h to yield PS-TEMPO-4-OH. The resultingpolystyrene was precipitated with methanol (300 mL) from a THF (50 mL)solution.

[0029] The product was then recrystallized twice from CH₂Cl₂ (40mL)/MeOH (200 mL) mixed solution, and collected by vacuum filtration togive white solids. The final solid was washed by 100 mL MeOH and driedin vacuo overnight to form PS-2 [yield: 32.6 g (78%). Mn=20900 andPDI=1.17. ¹H NMR (CDCl₃): 6.46-7.09 (br, 5H, ArH), 1.84 (br, 1H, CH),1.42 (br, 2H, CH₂)]. All manipulations were carried out under a drynitrogen atmosphere. Solvents, benzoyl peroxide, styrene, L-lactide, anddeuterated solvents were purified before uses.

EXAMPLE 2

[0030] Synthesis of Block Copolymers of Polystyrene-Poly(L-Lactide)(PS-b-PLA, or CP-4)

[0031] A typical ring-opening polymerization procedure was exemplifiedby the synthesis of CP-4. [(η₃-EDBP)Li₂]₂[(η₃-^(n)Bu)Li(0.5Et₂O)]₂ (0.11g, 0.1 mmol) was added to 4-hydroxy-TEMPO-polystyrene (PS-2, 4.18 g, 0.2mmol) in 20 mL of toluene at 0° C. The mixture was stirred at roomtemperature for 2 h, and then dried under vacuum. The resulting product(lithium alkoxide macroinitiator) was dissolved in CH₂Cl₂ (20 mL) andL-lactide (2.16 g, 15 mmol) in CH₂Cl₂ (10 mL) was added. While themixture was stirred for 4 h, conversion yield (74%) of poly(L-lactide)was analyzed by ¹H NMR spectroscopic studies.

[0032] The mixture was then quenched by the addition of an aqueousacetic acid solution (0.35 N, 20 mL) and the polymer was precipitated onpouring into n-hexane (300 mL) to give white solids. The product waspurified by precipitation from CH₂Cl₂ (30 mL)/Hexane (150 mL) mixturesolution. The final crystalline solid was precipitated from CH₂Cl₂ (30mL)/MeOH (150 mL) and dried under vacuum at 50-60° C. overnight to yield3.02 g of PS-b-PLA(CP-4) (yield: 48%). Mn=46700 and PDI=1.17. ¹H NMR(CDCl₃): 6.46-7.09 (br, 5H, ArH), 5.16 (q, 1H, CH(CH₃), J=7.2 Hz), 1.84(br, 1H, CH), 1.58 (d, 3H, CH(CH₃), J=7.2 Hz), 1.42 (br, 2H, CH₂). ¹Hand ¹³C NMR spectra were recorded on a Varian VXR-300 (300 MHz for ¹Hand 75 MHz for ¹³C) or a Varian Gemini-200 (200 MHz for ¹H and 50 MHzfor ¹³C) spectrometer with chemical shifts given in ppm from theinternal TMS or the central line of CHCl₃. The GPC measurements wereperformed on a Hitachi L-7100 system equipped with a differentialBischoff 8120 RI detector using THF (HPLC grade) as an eluent. Molecularweight and molecular weight distributions were calculated usingpolystyrene as standard.

[0033] A number of poly(styrene)-poly(L-lactide) (PS-PLLA) chiral blockcopolymers were prepared. On the basis of molecular weight and volumeratio, these PS-PLLAs are designated as PSxx-PLLAyy (ƒ_(PLLA) ^(ν)=z),wherein xx and yy represent the molecular weight of PS and PLLA dividedby one thousand measured by NMR, respectively, and z indicates thevolume fraction of PLLA. In these calculations, the densities of PS andPLLA are assumed to be 1.02 and 1.18 g/cm³, respectively.

EXAMPLE 3

[0034] Synthesis of Block Copolymers of PS280PLLA127

[0035] Another series of PS-PLLA copolymers with different volume ratioswere prepared by the same two-step “living” polymerization sequence. Onthe basis of molecular weight and volume ratio, these PS-PLLAs weredesignated as PSx-PLLAy (ƒ_(PLLA) ^(ν)=z), with x and y representing thenumbers of the repeating unit for PS and PLLA blocks and z representingthe volume fraction of PLLA (calculated by assuming that densities of PSand PLLA were 1.02 and 1.18 g/cm³, respectively). Bulk samples of theblock copolymers were prepared by solution casting from dichloromethane(CH₂Cl₂) solution (10 wt % of PS-PLLA) at room temperature.

EXAMPLE 4

[0036] Transmission Electron Microscopy (TEM) and Small-Angle X-rayScattering (SAXS) Studies

[0037] Crystallization of PLLA in PS-PLLA gave rise to significantchanges for microphase-separated morphology of PS-PLLA as observed inour laboratory. It is possible to destroy the formed microstructures soas to form crystalline morphology. DSC experiments were carried out in aPerkin Elmer DSC 7. For instance, PLLA blocks of PS29-PLLA22 (ƒ_(PLLA)^(ν)=0.37) melt at around 165° C. The maximum crystallization rate ofPLLA blocks is at ca. 95° C. in accordance with exothermic response(i.e., the occurrence of crystallization) at different isothermalcrystallizations. However, no significant exothermic response wasobserved under fast cooling. The glass transition temperatures of PLLAand PS are approximately 51.4° C. and 99.2° C., respectively.

[0038] SAXS experiments were conducted at the synchrotron X-raybeam-lineX3A2 at the National Synchrotron Light Source in Brookhaven NationalLaboratory. The wavelength of the X-ray beam is 0.154 nm. The zero pixelof the SAXS patter was calibrated using silver behenate, with thefirst-order scattering vector q* (q*=4λ⁻¹ sin θ, where 2θ is thescattering angle) being 1.076 nm⁻¹. Time-resolved SAXS experiments werecarried out in a heating chamber with step temperature increasing.Degradation temperature was identified by the disappearance ofscattering peaks.

[0039] DSC thermogram appeared no melting endotherm during heating. WAXD(Widel-Angle X-ray Diffraction) diffraction exhibited amorphousdiffraction profile. A Siemens D5000 1.2 kW tube X-ray generator (CuK_(α) radiation) with a diffractometer was used for WAXD powderexperiments. The scanning 2θ angle ranged between 5° and 40° with a stepscanning of 0.05° for 3 sec. The diffraction peak positions and widthsobserved from WAXD experiments were carefully calibrated with siliconcrystals with known crystal size.

[0040] Transmission electron microscopy in bright field was performedwith JEOL TEM-1200× transmission electron microscopy. Staining wasaccomplished by exposing the samples to the vapor of a 4% aqueous RuO₄solution for 3 hours.

[0041] The surface of the solution-casting PS-PLLA samples afterhydrolysis was observed using AFM (Atomic Force Microscopy). A SeikoSPA-400 AFM with a SEIKO SPI-3800N probe station was employed at roomtemperature in this work. A rectangle-shaped silicon tip was applied indynamic force mode (DFM) experiments using a type of SI-DF20 with aspring force contact of 19 Nm⁻¹ and scan rate of 1.0 Hz.

[0042] Field emission scanning electron microscopy was used to observethe PS-PLLA samples from different views. Field emission scanningelectron microscopy (FESEM) was performed on a Hitachi S-900 FE-SEMusing accelerating voltages of 2-5 keV. Samples were examined either onthe solution-cast surface or fractured cross sections of PS-PLLA thinfilms after hydrolysis. The samples were mounted to brass shims usingcarbon adhesive, and then sputter-coated with 2-3 nm of gold (the goldcoating thickness is estimated from a calculated deposition rate andexperimental deposition time).

EXAMPLES 5-8

[0043] Preparations of Varieties of PS-PLLA Having Hexagonal CylindricalNanostructures

[0044] A variety of PS-PLLA bulk samples were prepared by solutioncasting from dichloromethane (CH₂Cl₂) solution (10 wt % of PS-PLLA) atroom temperature. Table 1 shows the number-average molecular weights(Mn), polydiversity (PDI), volume fraction of polystyrene, ƒ_(PS) ^(ν),d-spacing, and diameter of the samples so prepared. The number-averagemolecular weight of each component of the copolymers was measured fromintegration of ¹H NMR measurement. The polydipersity was obtained fromGPC analysis. The values listed under column [c] were obtained fromcalculation of TEM micrographs. The values listed under column [d]determined from first scattering peak of SAXS. And the values listedunder column [e] were obtained from surface analysis of scanning probemicroscopy (SPM). PS-PLLA Mn,_(PS) Mn,_(PLLA) d-spacing [nm] Diameter[nm] Copolymer [g/mol] [g/mol] PDI f_(PS) ^(ν) [c] [d] [e] [c] [d] [e]PS83-PLLA41 8900 5900 1.15 0.64 12.7 16.8 20.8 7.2 12.2 10.1PS198-PLLA71 20700 10200 1.17 0.70 25.8 28.4 32.9 13.8 18.9 19.7PS280-PLLA97 29400 14000 1.21 0.73 31.4 37.2 35.5 16.7 23.5 20.0PS365-PLLA109 38200 15700 1.21 0.74 34.1 39.7 44.2 17.0 24.6 20.9

[0045]FIGS. 1A and 1B show that hexagonal cylinder nanostructures ofamorphous PS-PLLA were identified by Transmission electron microscopy(TEM), and small-angle X-ray scattering (SAXS), respectively. Similarresults for various PS-PLLA samples as provided in Table 1 havingdifferent molecular weights were also obtained. Thin films of the blockcopolymer were formed on different substrates by simply spin coatingfrom dilute chlorobenzene (C₆H₅Cl) solution (1.5 wt % of PS-PLLA) atroom temperature without further treatment.

[0046]FIG. 2A shows that well-oriented, perpendicular microdomains wasobtained as evidenced by scanning probe microscopy (SPM). FIG. 2B showsthat the effect of alignment was further confirmed by the TEM imageswhere the projected images reflected perpendicular cylinders on thesubstrate. As evidenced by selected area electron diffractionexperiments, no crystalline diffraction was identified; suggesting thatamorphous or low crystallinity samples were obtained after spin coating.With the process of the present invention, the oriented microdomains canbe as large as several cm² in area.

[0047] The method of the present invention can be tailored for greatvarieties of end use applications. For example, different substratesincluding glass slide, carbon-coated glass slide, indium tin oxide (ITO)glass, silicon wafer, silicon oxide, inorganic light emitted diode andalumina have been used for nanopatterning. Large-size, orientedperpendicular hexagonal cylinder morphology was obtained. However, thebottom morphology of the nanopatterns appeared well-definednanostructures under SPM examination only if the film was treated byhydrolysis (i.e., degradation of PLLA); suggesting that there is alwaysa thin layer of PLLA formed on the substrate after spin coating (forinstance, ca. 5 nm as estimated by volume fraction for cast film onglass slide having 50 nm thickness). Similar to the recent studies ofelectric field alignment of block copolymers; the surface effect fromcoated substrate on morphology is always existent. The effects ofsubstrate affinity and interfacial energy have been examined in thisstudy. The surface tension of PLLA (˜38.27 mN/m) is lower than that ofPS (˜40 mN/m) besides the affinity of PLLA with hydrophilic substrate isslightly higher than that of PS. As a result, PLLA favors topreferentially segregate on the substrate so as to form PLLA thin layer.The formation of PLLA thin layer can be avoided by spin-coating thesamples at temperature above T_(g,PLLA) but below T_(g,PS). The behaviorhas also been observed in different cases; the glass transitiontemperature of at least one of the blocks should be below processingtemperature in order to ease the substrate influence. As a result, thenanopatterned textures were thus schematically illustrated in FIG. 3A.Furthermore, the oriented nanostructures started losing orientationafter long-time annealing at temperature above PLLA crystalline melting.As a result, we speculate that the ignorance of substrate effect is dueto the kinetic effect under spinning to create a meta-stable morphology.Nevertheless, the oriented nanostructures can be fixed by simplyoxidizing the PS matrix using RuO₄. After oxidation, the PS nanopatternscan be used at service temperatures above 250° C. Our preliminaryresults indicate that the oriented effect for block copolymernanostructures is primarily attributed to the selection of appropriatesolvent evaporation rate and its solubility between constituted blocks.Similar to solution casting approach, oriented perpendicular Hexagonalcylinder morphology was formed at intermediate evaporation rate forselective solvent.

[0048]FIG. 3A is an illustrative 3-D diagram showing the nanopatternsthat are produced using the method of the present invention. The methodof the present invention can be utilized to extend the applicability ofnanopatterns. It is possible to have tunable film thickness anddimension for nanopatterning. Reasonably wide range of film thicknessfrom 20 nm to 160 nm can be obtained by simply controlling the spin rateof coating as expected. Oriented PS-PLLA samples can be achievedregardless of thin-film thickness. Also, the surface topography offormed nanopatterns is very smooth; the averaged roughness is in therange of 0.4 nm by SPM roughness evaluation. Different domain sizes asdetermined by TEM, SAXS and SPM were obtained by controlling molecularweight of PS-PLLA. FIGS. 3B and 3C show that, following the successfulprocedure for hydrolysis of PLA, well-oriented, perpendicular hexagonalcylinder nanochannel arrays were simply obtained within hour by using asodium hydroxide solution of methanol/water (0.5M solution was preparedby dissolving 2 g of sodium hydroxide in an 40/60 (by volume) solutionof methanol/water) at 60° C. for the degradation of amorphous PLLA.Consequently, nanopatterned templates over large area in addition touniform surface with controlled thickness and domain size in the form ofthin films were successfully prepared on different substrates.

[0049]FIGS. 4A, 4B, and 4C show the TEM micrographs of solution-cast of(a) PS83-PLLA41 (ƒ_(PLLA) ^(ν)=0.34); (b) PS198-PLLA71 (ƒ_(PLLA)^(ν)=0.27) and (c) PS280-PLLA97 (ƒ_(PLLA) ^(ν)=0.31) bulk samplesquenched from microphase-separated melt, respectively. The samples weremicrosectioned by microtome, and then stained by RuO₄ to obtainmass-thickness contrast. The corresponding azimuthally scannedone-dimensional SAXS profiles are also obtained as shown in FIGS. 4D,4E, and 4F, respectively.

[0050]FIGS. 5A, 5B, 5C, and 5D show the tapping-mode SPM phase images ofthe surfaces of spin-coated PS365-PLLA109 (ƒ_(PLLA) ^(ν)=0.26) thinfilms on (a) glass slide; (b) carbon-coated glass slide; (c) indium tinoxide (ITO) glass; (d) silicon wafer.

[0051]FIGS. 6A and 6B show the tapping-mode SPM height images of thebottom morphology for spin-coated PS365-PLLA109 (ƒ_(PLLA) ^(ν)=0.26)thin film on glass slide (a) before hydrolysis; and (b) afterhydrolysis, respectively.

[0052]FIGS. 7A, 7B, 7C, and 7D show the tapping-mode SPM phase images ofthe surfaces of spin coated PS365-PLLA109 (ƒ_(PLLA) ^(ν)=0.26) thinfilms on glass slide by using different solvents for spin coating: (a)dichlorobenzene (vapor pressure at 20° C.: 0.52 mm Hg); (b)chlorobenzene (vapor pressure at 20° C.: 12 mm Hg); (c) toluene (vaporpressure at 20° C.: 22 mm Hg); (d) THF (vapor pressure at 20° C.: 131.5mm Hg), respectively.

[0053]FIGS. 8A, 8B, and 8C show the tapping-mode SPM phase images of thesurfaces of spin coated PS365-PLLA109 (ƒ_(PLLA) ^(ν)=0.26) thin films onglass slide from chlorobenzene with different thin-film thickness: (a)160 nm; (b) 80 nm; (c) 50 nm; (d) 30 nm, respectively.

[0054]FIG. 9A shows the plot of film thickness versus spin rate forspin-coated PS365-PLLA109 (ƒ_(PLLA) ^(ν)=0.26) thin films on glassslides. Open circle indicates the sample thickness measured by SPMwhereas open triangle indicates the thickness measured by depthprofiler. FIG. 9B shows the 3D tapping-mode SPM height image of SPM forspin-coated PS365-PLLA109 (ƒ_(PLLA) ^(ν)=0.26) thin film afterhydrolysis.

[0055] Finally, FIGS. 10A and 10B show FESEM micrographs of hydrolyzedPS365-PLLA109 (ƒ_(PLLA) ^(ν)=0.26) samples by viewing parallel to thecylindrical axes.

[0056] As discussed above, the present invention discloses an efficientand cost-effective way to prepare large-scale microdomains from PS-PLLAdiblock copolymers. Owing to the hydrolysis character of the polyestercomponents, the formation of the ordered nanohole arrays provides asimple path to prepare nanopatterned templates for nanoapplications.

What is claimed is:
 1. A method for manufacturing nanoscale objectscomprising the steps of: (a) obtaining a nanopatterned template andusing said nanopatterned template to form nanoscale objects; (b) whereinsaid nanopatterned template is formed using the method comprising thesteps of: (i) using a block copolymerization process to prepare a blockcopolymer comprising first and second polymer blocks, said first andsecond polymer blocks being incompatible with each other; (ii) forming athin film under conditions such that said first polymer blocks form intoa periodically ordered topology; and (iii) selectively degrading saidfirst polymer blocks to cause said thin film to become a nanoporousmaterial with a periodically ordered porous geomorphology.
 2. The methodfor manufacturing nanoscale objects according to claim 1 wherein saidfirst polymer blocks have a hexagonal cylindrical geomorphology with itsaxis perpendicular to a surface of said thin film.
 3. The method formanufacturing nanoscale objects according to claim 1 wherein said firstpolymer is selected from the group consisting of poly(L-lactide),poly(D-lactide), poly(lactide), poly(acprolactone), and said secondpolymer is selected from the group consisting of poly(styrene),poly(vinylpyridine), and poly(acrylonitile).
 4. The method formanufacturing nanoscale objects according to claim 1 wherein said blockcopolymer is poly(styrene)-poly(L-lactide) (PS-PLLA) chiral blockcopolymer, said first polymer is poly(L-lactide), and said secondpolymer is polystyrene.
 5. The method for making a series of nanoscaleobjects according to claim 1, wherein said block copolymer ispoly(4-vinylpyridine)-poly(L-lactide) (P4VP-PLLA) chiral blockcopolymer, said first polymer is poly(L-lactide), and said secondpolymer is pol(4-vinylpyridine).
 6. The method for making a series ofnanoscale objects according to claim 1, wherein said block copolymer ispoly(acrylonitrile)-poly(caprolactone) (PVHF-PCL) block copolymer, saidfirst polymer is poly(caprolactone), and said second polymer ispol(acrylonitrile).
 7. The method for making a series of nanoscaleobjects according to claim 1, wherein said thin film is formed on asubstrate selected from the group consisting of glass slide,carbon-coated glass slide, indium tin oxide (ITO) glass, silicon wafer,silicon oxide, inorganic light emitted diode and alumina.
 8. The methodfor making a series of nanoscale objects according to claim 1, whereinsaid thin film is formed on a substrate by spin coating.
 9. The methodfor making a series of nanoscale objects according to claim 1, whereinsaid periodically ordered topology of said first polymer blocks isformed by controlled solution casting, shield fields, electric fields,patterned substrates, temperature gradients, or epitaxialcrystallization.
 10. The method for making a series of nanoscale objectsaccording to claim 1, wherein first polymer blocks are selected degradedby hydrolysis.
 11. A nanopatterned template for use in manufacturingnanoscale objects, said nanopatterned template comprises a nanoporousthin film with a periodically ordered porous geomorphology, wherein saidnanoporous thin film is made from a process comprising the steps of: (a)using a block copolymerization process to prepare a block copolymercomprising first and second polymer blocks, said first and secondpolymer blocks being incompatible with each other; (b) forming a thinfilm under conditions such that said first polymer blocks form into aperiodically ordered topology; and (c) selectively degrading said firstpolymer blocks to cause said thin film to become a nanoporous materialwith a periodically ordered porous geomorphology.
 12. The nanopatternedtemplate according to claim 11 wherein said first polymer blocks have ahexagonal cylindrical geomorphology with its axis perpendicular to asurface of said thin film.
 13. The nanopatterned template according toclaim 11 wherein said first polymer is selected from the groupconsisting of poly(L-lactide), poly(D-lactide), poly(lactide),poly(acprolactone), and said second polymer is selected from the groupconsisting of poly(styrene), poly(vinylpyridine), andpoly(acrylonitile).
 14. The nanopatterned template according to claim 11wherein said block copolymer is poly(styrene)-poly(L-lactide) (PS-PLLA)chiral block copolymer, said first polymer is poly(L-lactide), and saidsecond polymer is polystyrene.
 15. The nanopatterned template accordingto claim 11, wherein said block copolymer ispoly(4-vinylpyridine)-poly(L-lactide) (P4VP-PLLA) chiral blockcopolymer, said first polymer is poly(L-lactide), and said secondpolymer is pol(4-vinylpyridine).
 16. The nanopatterned templateaccording to claim 11, wherein said block copolymer ispoly(9-vinyl-9H-fluorene)-poly(caprolactone) (PVHF-PCL) block copolymer,said first polymer is poly(caprolactone), and said second polymer ispol(9-vinyl-9H-fluorene).
 17. The nanopatterned template according toclaim 11, wherein said thin film is formed on a substrate selected fromthe group consisting of glass slide, carbon-coated glass slide, indiumtin oxide (ITO) glass, silicon wafer, silicon oxide, inorganic lightemitted diode and alumina.
 18. The nanopatterned template according toclaim 11, wherein said thin film is formed on a substrate by spincoating.
 19. The nanopatterned template according to claim 11, whereinsaid periodically ordered topology of said first polymer blocks isformed by controlled solution casting, shield fields, electric fields,patterned substrates, temperature gradients, or epitaxialcrystallization.
 20. The nanopatterned template according to claim 11,wherein first polymer blocks are selected degraded by hydrolysis.